A Mysterious Sinkhole Found--What is it?

In this video I found a large sinkhole out in the woods. It looks very much like a the sort of sinkhole that a cave would be under, but when I dug it out and pounded a pole down into it, I found just a bunch of sand. This makes me think that is most likely a sandpit or something down that line or a place where the sand compacted and collapsed onto itself, leaving a sinkhole.